U.S. Pat. No. 4,873,197 and 5,010,020 disclose processes for quick color tests for detecting the presence of lead in glaze and enamel coatings as well as kits which can be used in making such tests. To this end, a sample is first washed with a detergent. The surface of the sample is then contacted with a slip of filter paper wet with a solution of citric or formic acid. After a suitable time period, the paper slip is spotted with a liquid chromogen. The formation of a rose or rose/red stain signifies that the tested coating has an releasable amount of lead. A suitable test kit for performing such tests consists of absorbent paper strips, an aqueous solution of a suitable acid, distilled water and a rhodizonic acid dipotassium salt. The salt is deliquescent and deteriorates in air in the presence of moisture and must be dissolved in the water just before used as a liquid.
After it was recognized that excess lead in painted surfaces could also be harmful, it was found that neither the kit nor the test described above could be used without modification to identify the presence or absence of lead in painted surfaces. Accordingly a new test and suitable kit were developed.
This kit employs a non-porous card having one or more small sections with circular coatings of a solid rhodizonic acid dipotassium salt chromogen. In use, the tip of a cotton swab is charged with a liquid acid and a small sample of the painted surface being tested and then is moved into contact with this chromogen coating to test for the presence of lead. When the chromogen coating is in proper condition, the color change of this chromogen indicates the presence of lead. The coatings of the rhodizonic salt are prepared by dissolving the salt and a sodium acetate buffer in water then immediately applying this solution to the card as a coating which is then dried. The card is packaged inserted in the package. However, because of unpredictable variations in the moisture content and the absorbent properties of the desiccant, this package has a variable and unpredictable useful life since the chromogen coating may be contaminated with entrapped moisture. Thus the useful life of this kit is also variable and unpredictable.
The present invention is directed toward a package containing a card with coatings of a rhodizonic salt which is not contaminated with water and thus is more stable and less variable as well as a process for producing this card.